Polyhalogen Compounds Class 12 Notes | EduRev

Chemistry Class 12

Created by: Mohit Rajpoot

Class 12 : Polyhalogen Compounds Class 12 Notes | EduRev

The document Polyhalogen Compounds Class 12 Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
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Polyhalogen derivatives:

Trichloromethane (Chloroform), CHCl3

Preparation:

CH4 + Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CH3Cl + HCl
                              Chloromethane

CH3Cl + Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CH2Cl2 + HCl
                                  Dichloromethane

CH2Cl2 + Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CHCl3 + HCl
                                    Trichloromethane

CHCl3 + Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CCl4 + HCl
                                Tetrachloromethane

The mixture of CH3Cl, CH2Cl2, CHCl3 and CCl4 can be separated by fractional distillation.

2. From chloral hydrate, Pure chloroform can prepare.

NaOH + CCl3CHO → HCOONa + CHCl3
                                      chloral

NaOH + CCl3CH(OH)2 → HCOONa + CHCl3 + H2O
Chloral hydrate               sodium formate Chloroform

3. Laboratory Method : From ethanol or acetone, by reaction with a paste of bleaching powder and water.

In case of ethanol, the reaction occurs as follows:

CaOCl2 + H2O → Ca(OH)2 + Cl2

CH3CH2OH + Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CH3CHO + 2HCl

CH3CHO + 3Cl2 Polyhalogen Compounds Class 12 Notes | EduRev CCl3CHO + 3HCl

                                                              Chloral

Ca(OH)2 + 2CCl3 CHO Polyhalogen Compounds Class 12 Notes | EduRev 2CHCl3 + (HCOO)2Ca

                                                               Chloroform Calcium formate

4. From carbon tetrachloride:

CCl4 + 2[H] Polyhalogen Compounds Class 12 Notes | EduRev CHCl3 + HCl (partial reduction)

5. Haloform reaction:

Polyhalogen Compounds Class 12 Notes | EduRev

Polyhalogen Compounds Class 12 Notes | EduRev (Haloform)

Step 1 : Attack of the

Step 2 : Elimination

Step 3 : Proton transfer

nucleophile of the leaving group

Prob. Compare rate of elimination (Dehydro halogenation in presence of alcoholic KOH ) i.e., E2 :

1. (a) Polyhalogen Compounds Class 12 Notes | EduRev (b) Polyhalogen Compounds Class 12 Notes | EduRev (c) Polyhalogen Compounds Class 12 Notes | EduRev (d) Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a > d

2. (a) Polyhalogen Compounds Class 12 Notes | EduRev (b) Polyhalogen Compounds Class 12 Notes | EduRev (c) Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a

3. (a) Polyhalogen Compounds Class 12 Notes | EduRev (b) Polyhalogen Compounds Class 12 Notes | EduRev (c) Polyhalogen Compounds Class 12 Notes | EduRev

c > b > a

4. (a) Polyhalogen Compounds Class 12 Notes | EduRev (b) Polyhalogen Compounds Class 12 Notes | EduRev (c) Polyhalogen Compounds Class 12 Notes | EduRev

b > a > c

Dehalogenation : - (-X2) E2

Polyhalogen Compounds Class 12 Notes | EduRev

Dehalogenation : - (-X2) E2

Polyhalogen Compounds Class 12 Notes | EduRev

Polyhalogen Compounds Class 12 Notes | EduRev

 

Ec or Ei (Intramolecular or cyclic elimination mechanism):

(1) Lg and Base present in same molecule.

(2) It proceeds by cyclic transition state.

(3) Overall it is syn elimination.

(4) Hoffmann is major product as it is obtained by least hindered site of cyclic transition state.

(5) No rearrangement.

Example of Ec/Ei:

Pyrolysis of Ester:

Polyhalogen Compounds Class 12 Notes | EduRev

              Polyhalogen Compounds Class 12 Notes | EduRev                                                 Polyhalogen Compounds Class 12 Notes | EduRev

Polyhalogen Compounds Class 12 Notes | EduRev

1. Polyhalogen Compounds Class 12 Notes | EduRev

2. Polyhalogen Compounds Class 12 Notes | EduRev

1.8.2 Physical properties of chloroform

Chloroform is a colourless, heavy liquid which has sweetish, sickly odour and taste. It boils at 334º K and is slightly soluble in water. It is heavier than water. As inhaling of the vapours of chloroform induces unconsciousness therefore it can be used as an anaesthetic agent for surgery. 

1.8.3 Chemical properties of chloroform:

1. Action of sun light and air-

2 CHCl3 + O2 Polyhalogen Compounds Class 12 Notes | EduRev 2COCl2 + 2HCl

Phosgene

As chloroform is used for anaesthetic purposes, therefore in order to maintain a high purity of chloroform, this reaction can be avoided by storing it in dark bottles, completely filled upto the brim. The use of dark bottles (brown or blue) cuts off active light radiations and filling upto brim keeps out air. Apart from this a small amount of ethanol (1%) is usually added to bottles of chloroform. Addition of a little ethanol fixes the toxic COCl2 as non-poisonous diethyl carbonate.

COCl2 + 2C2H5OH Polyhalogen Compounds Class 12 Notes | EduRev O = C(OC2H5) + 2HCl

diethyl carbonate

2. Hydrolysis :

H - CCl3 + (aq.) 3KOHPolyhalogen Compounds Class 12 Notes | EduRev Polyhalogen Compounds Class 12 Notes | EduRev HCOOK

3. Reduction :

Zn + 2HCl Polyhalogen Compounds Class 12 Notes | EduRev ZnCl2 + 2[H]

CHCl3 + 2[H] Polyhalogen Compounds Class 12 Notes | EduRev CH2Cl2 + HCl
                                Dichloromethane
                              (Methylene chloride)

CHCl3 Polyhalogen Compounds Class 12 Notes | EduRev CH4 + 3HCl

4. Reaction with acetone :

(CH3)2C = O + CHCl3 Polyhalogen Compounds Class 12 Notes | EduRev Polyhalogen Compounds Class 12 Notes | EduRev

                                                                     Chlroetone

Use : Chloretone is used as hypnotic (a sleep inducing) drug.

5. Reaction with nitric acid:

2CHCl+ HONO2 Polyhalogen Compounds Class 12 Notes | EduRev CCl3. NO2 + H2O
                                               (Chloropicrin)

Use: Chloropicrin is used as an insecticide and war gas.

6. Reaction with silver powder :

Polyhalogen Compounds Class 12 Notes | EduRev

7. Chlorination :

CHCl3 + Cl2 Polyhalogen Compounds Class 12 Notes | EduRevCCl4 + HCl

8. Reimer-Tiemann reaction:

Polyhalogen Compounds Class 12 Notes | EduRev + CHCl3 + 3NaOH Polyhalogen Compounds Class 12 Notes | EduRev Polyhalogen Compounds Class 12 Notes | EduRev + 2NaCl + 2H2O

1.8.4 Uses of chloroform

1. As solvent in oils and varnishes.

2. As preservative for anatomical specimens.

3. As laboratory reagent.

4. As an anesthetic.

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